So you're wanting a musette bag that can be worn as a backpack? This is $36. I have a similar old army medic bag and canvas is actually a great material.
U.S. WW2 M1936 Musette Bag with Shoulder Strap-Dark OD 1944
https://www.etsy.com/listing/811177303/us-ww2-m1936-musette-bag-with-shoulder?gpla=1&gao=1&&utm_source=google&utm_medium=cpc&utm_campaign=shopping_us_b-art_and_collectibles-collectibles-memorabilia-militaria&utm_custom1=_k_Cj0KCQjwnJaKBhDgARIsAHmvz6eqAuSe7FozBZlpzIYaEliPOfiAg_HlYtvtNElDqUieO-1z_n4CDokaAqgAEALw_wcB_k_&utm_content=go_12569400376_122439143711_507438087800_pla-316730450633_c__811177303_249710056&utm_custom2=12569400376&gclid=Cj0KCQjwnJaKBhDgARIsAHmvz6eqAuSe7F ozBZlpzIYaEliPOfiAg_HlYtvtNElDqUieO-1z_n4CDokaAqgAEALw_wcB
